Unwanted plants, such as weeds, reduce the amount of resources available to crop plants and can have a negative effect on crop plant yield. Commonly unwanted plants in crop plant environments include broadleaf plants and grasses.
Herbicides are used to kill unwanted plants, such as weeds, in crop plant environments. Herbicides are expensive, and their use may result in unintentional consequences such as groundwater contamination, environmental damage, herbicide-resistant weeds, and human and mammalian health concerns. It is therefore desirable to minimize the amount of herbicides applied to a crop-growing environment or any area in need of weed control.
Unwanted plants, such as weeds, may greatly reduce yields of crop plants. For example, a Horseweed infestation reportedly was responsible for an 80% reduction in soybean yields. Bruce, J. A., and J. J. Kells, Horseweed (Conyza Canadensis) control in no-tillage soybeans (Glycine max) with preplant and preemergence herbcides, Weed Technol. 4:642-647 (1990). Therefore, controlling weeds, and especially grasses and Horseweed, is a major concern of crop growers.
Further, Horseweed and other grasses are becoming resistant to the widely used herbicide glyphosate. As early as 2000, glyphosate resistant Horseweed was reported in Delaware. Glyphosate resistant Horseweed has since been reported in numerous states. Accordingly, there is a need for new products that can provide effective kill rates of glyphosate resistant Horseweed.
Weeds are also becoming resistant to herbicides that inhibit acetolactate synthase (ALS) and protoporphyrinogen oxidase (PPO). Horseweed has also been reported to be resistant to 2,4-D and dicamba. Accordingly, there is a need for new technology to control weeds that are resistant to commercially available herbicides.
In most fields throughout the Midwest and Mid-South, in-crop burndown applications are the only options for controlling weeds due to weather and timeliness of applications. Growers often find an active ingredient that is effective and the use it repeatedly. Eventually, the weeds become resistant to the active ingredient which leaves no alternatives for weed control other than mechanical removal. Mechanical removal of weeds requires extensive use of resources and is not an option for no-till or highly erodible land.
No-till farming has been increasing in popularity because it has many benefits, including decreased labor time and decreased soil erosion. However, one of the downsides of no-till farming is that weeds are harder to control in these areas because they are not subjected to tilling. Accordingly, there is an increasing need for alternative ways to handle weed infestation.
Pyroxasulfone (3-[[[5-(difluoromethoxy)-1-methyl-3 (trifluoromethyl)-1H-pyrazol-4-yl]methyl]sulfonyl]-4,5-dihydro-5,5-dimethylisoxazole) is an herbicide that has residual weed control. Pyroxasulfone, however, does not have post emergence weed control. Pyroxasulfone is commercially available in a mixture with flumioxazin (Fierce®, available from Valent U.S.A. Corporation).
Plant cell membrane disruptor herbicides' work by causing destruction of cell membranes which results in cell content leakage. These herbicides are primarily contact herbicides and have very limited translocation through the plant. Plant cell membrane disruptor herbicides can be sub-divided into diphenylethers, N-phenyl-phthalimides, and aryl triazolinones or photosystem I electron diverter such as bipyridyliums.
Diphenylether herbicides are inhibitors of photoporphyrinigen oxidase (PPO) within the plant. Diphenylether herbicides include fomesafen, lactofen, acifluorfen, and oxyfluorfen. When applied alone, diphenylether herbicides often yield unsatisfactory weed control. To overcome this, diphenylether herbicides are sometimes applied with S-metochlor or acetochlor to increase effectiveness. However, the efficacy of such combinations is often not satisfactory and high application rates are still required to achieve acceptable control of grass weeds and broadleaves. Moreover, the reliability of such combinations depends strongly on the weathering conditions and certain difficult to control weed species may escape. In addition, the herbicidal activity of these compositions persists only for a short time, which allows effective burndown only within a small timeframe prior to planting a crop. Moreover, the persistence of the herbicidal activity strongly depends upon the weathering conditions.
S-metolochlor and acetochlor are chloroacetanilide herbicides and work by interfering with enzymes in the gibberellin pathway. There is a current desire to minimize the use of these herbicides due to environmental concerns.
N-phenyl-phthalimide herbicides are also PPO inhibitors. N-phenyl-phthalimide herbicides include cinidon-ethyl, flumioxazin, and flumiclorac-pentyl.
Triazolinone herbicides are another class of PPO inhibitors. Triazolinone herbicides include azafenidin, carfentrazone-ethyl, and sulfentrazone.
Bipyridylium herbicides interfere with electron transfer and use uncoupled electrons to form reactive superoxides. Bipyridylium herbicides include paraquat and diquat.
U.S. Patent Application Publication No. 2011/0065579 discloses thousands of mixtures of herbicides, one of which is a mixture of glyphosate or glufosinate with pyroxasulfone in a ratio range of from 2000:1 to 1:10 which can also include a cell membrane disruptor. However, this publication fails to provide guidance within this broad range of acceptable amounts of the herbicides. Further, this publication does not teach or suggest narrower ratios that would produce acceptable results. In addition, this publication fails to suggest the synergy that Applicants discovered between plant cell membrane disruptors and pyroxasulfone.
U.S. Patent Application Publication No. 2011/0015068 discloses mixtures of pyroxasulfone with PPO inhibitors. This publication, however, fails to suggest synergistic ratios between pyroxasulfone and diphenylether, N-phenyl-phthalimide, triazolinone, or bipyridylium plant cell membrane disruptor herbicides.
Anthem® (available from FMC Corporation) is a product that comprises pyroxasulfone and fluthiacet, a PPO inhibitor. Fluthiacet, however, has had limited postemergence herbicidal activity in addition to having no postemergence herbicidal activity as it pertains to the pyroxasulfone component.
In summary, there is a need for a composition that reduces the amount of herbicides necessary to obtain sufficient weed control while minimizing the harm to crop plants. As more weeds become resistant to herbicides, alternative compositions with high weed control are desired. Further, as no-till farming continues to increase in popularity, there is a greater need for effective herbicides. A composition with effective weed control and lower dosage rate will lead to increased crop plant yields, and decreased environmental, human, and mammalian health concerns.